Add test-requirements.txt

The central place for all testing requirements. And use it everywhere.
Fix all PEP-8 / flake8 code issues

Drop testscope because it's empty.
Name all tests consistently

Let all of them start with 'test_'. And move __main__.py into
__init__.py.
Refactor testsuite invocation

Move shared parts into test.core and use it in LESS, issues and
bootstrap3 auto-generated tests. This simplifies the test code and
allows to use nosetests (or any other test runner).
Drop 'pep8' tox target

We have flake8 which is a wrapper around pep8, pyflakes and mccabe.
Support publishing wheels

Lesscpy is currently pure-Python and works with both py2 and p3, so we
can publish universal wheels.

See http://pythonwheels.com/
Move bin/ to scripts/